The invention described herein relates generally to furnaces, and more particularly to a novel type of tube furnace, and methodology related thereto, that provides both temperature uniformity, over a long length and within a large volume, and very accurate and rapid, linear as well as non-linear, programmed heating capability.
Tube furnaces are well-known pieces of laboratory and industrial equipment. They usually comprise resistance-wound tubes of, for example, quartz or ceramic materials. Objects placed within the tube become heated when electrical current is applied to the furnace. Tube furnaces are commercially available from many manufacturing sources.
Drexel, in U.S. Pat. No. 4,348,580, issued Sept. 7, 1982, teaches a tubular furnace whose temperature controlled central region is bounded by at least one movable end wall. Isothermal conditions or temperature gradients are maintained by means of a temperature-sensing feed-back circuit. The furnace employs a central heater and two guard heaters that each are capable of independent electrical power control to provide independent resistance heating.
Yu et al., in U.S. Pat. No. 4,886,954, issued Dec. 12, 1989, discloses a hot wall furnace having a plurality of vertically adjacent electrical resistance heating elements that are wired in parallel. The plurality of resistance heating elements are disposed about the flat temperature zone of a processing chamber, for inputting different amounts of heat per unit area to adjacent segments of the zone.
Hicks, in U.S. Pat. No. 3,705,253, issued Dec. 5, 1972, discloses a furnace wall construction having a metal shell and inner fibrous insulating layer and resistance wire mounted inside the insulating layer.
Acker et al., in U.S. Pat. No. 4,367,866, issued Jan. 11, 1983, discloses a multilayer furnace construction for containment of molten metal with electrical conductors embedded in a particulate layer surrounding a removable inner vessel.
Giler, in U.S. Pat. No. 4,417,346, issued Nov. 22, 1983, and Sevink, in U.S. Pat. No. 4,486,888, issued Dec. 4, 1984, disclose other furnaces with heating coils on the inside surface.
In general, known tube furnaces are quite complex in having multi-component heating systems that are regulated by intricate and complicated control systems. Tube furnace designs offering improved simplicity, large-volume temperature uniformity, and fast and accurate programmed temperature control, would be welcomed as very beneficial in many areas of scientific and industrial research and engineering.